Re: linux-2.6.25: 'mkdir -p' does not work with rootdir as mount point inside a read only filesystem

["Dan Noé" <dpn@isomerica.net>]

Andrew Morton wrote:
>> |root@triton1:/# mount
>> |rootfs on / type rootfs (rw)
>> |/dev/root on / type jffs2 (ro)
>> |proc on /proc type proc (rw)
>> |sysfs on /sys type sysfs (rw)
>> |/dev/root on /dev/.static/dev type jffs2 (ro)
>> |tmpfs on /dev type tmpfs (rw,size=10240k,mode=755)
>> |tmpfs on /var type tmpfs (rw)
>> |tmpfs on /tmp type tmpfs (rw)
>> |devpts on /dev/pts type devpts (rw,gid=5,mode=620)
>> |tmpfs on /dev/shm type tmpfs (rw)
>> |root@triton1:/# mkdir -p /dev/.udev/db
>> |mkdir: Cannot create directory `/dev/': Read-only file system
>>
>> While:
>> |root@triton1:/# cd /dev
>> |root@triton1:/# mkdir -p .udev/db
>> works as expected...
>>
>> Has anyone else encountered this problem already?
>> I've searched the archives but could not find anything related to this
>> problem.
> 
> I had a shot at scripting this, but for me, everything works OK.
> 
> #!/bin/sh
> dd if=/dev/zero of=file1 bs=1M count=32
> dd if=/dev/zero of=file2 bs=1M count=32
> yes | mkfs -t ext2 file1
> yes | mkfs -t ext2 file2
> mkdir -p mountpoint
> mount -o loop file1 mountpoint
> mkdir mountpoint/dir
> umount mountpoint
> mount -o loop,ro file1 mountpoint
> mount -o loop file2 mountpoint/dir
> mkdir -p $(/bin/pwd)/mountpoint/dir/subdir

Hmmm.  The thing you are doing differently is that the reporter's root 
filesystem is mounted read only but in your case (and the quick try I 
had at it) the read only file system is mounted below root.

However, I tried reproducing that scenario with a chroot and I still 
couldn't get it to happen.  No time to try a real root mount ro this 
morning but perhaps others can.

Cheers,
Dan

-- 
                     /--------------- - -  -  -   -   -
                     |  Dan Noé
                     |  http://isomerica.net/~dpn/